Structure that counteracts biofouling in aquatic environments

ABSTRACT

The invention aims at a structure which counteract bio-fouling in aquatic environments and is principally characterized by the fact that the surface of an object has parallel ribs projecting from it ( 4, 5 ), close to each other, which are narrowing outward and whose height is less than two millimetres.

[0001] This invention has reference to counteracting bio-fouling on surfaces in aquatic environments by letting the surface have a ribbed structure.

[0002] Surfaces which are immersed into the sea will immediately be covered by bio-fouling. First a thin layer of bio-polymers, bacteria and unicellular algae is formed, followed by a thick layer of invertebrates for instance acorn barnacles and mussels. Such bio-fouling is a serious problem for shipping because the increased water resistance has an influence on the fuel consumption. Besides bio-fouling has negative consequences for flows through piping systems and for exchange speeds in heat exchangers. The marine cultivation industry is also affected negatively by bio-fouling. Net bags, cultivation cages, rafts and ropes will often be strongly overgrown which will cause increased mortality and high cleaning costs. Increased weight and cleaning as a result of bio-fouling are also problems within offshore industry.

[0003] The most frequent method to counteract bio-fouling is applying poisonous paints to the surfaces which are to be protected. Commercial shipping often uses TBT paints (Tributyltin) and pleasure boats in most cases copper-based paints. Increased environment-consciousness of the risk of spreading these very poisonous substances in the sea has resulted in local prohibitions against their use. Moreover a global restriction against the use of TBT paints for commercial shipping is expected to come into force in 2008.

[0004] The need of new environment-friendly solutions to prevent bio-fouling is obvious. On the Swedish west coast for instance the dominating problem is acorn barnacles. One method which does not include any chemical substances to reduce bio-fouling by acorn barnacles is providing surfaces with microstructures. In repeated experiments it has been observed that the larvae of acorn barnacles avoid surfaces with structures of a certain appearance. The mechanism is that the adhesion of the larvae is disturbed and interrupted and that the larvae actively choose to abandon the surface. Existing inventions which give this effect is providing surfaces with fibres which are glued at right angles out from the surface. Other existing methods are attaching a carrying layer of cloth with projecting fibres from the cloth or attaching a plastic film with thin plastic strips welded to it.

[0005] The invention has the special characteristics which are evident from the patent claims and will be explained more closely in the following by means of figures where examples are shown.

[0006]FIG. 1 shows a section of a foil greatly magnified.

[0007]FIG. 2 shows, greatly magnified, a ribbed structure directly on a surface which is to be protected.

[0008]1 indicates a carrying foil of plastic with a high melting-point. This foil is laminated with a second foil 2 of a more easily fusible plastic. 3 indicates a self-adhesive glue. From the easily fusible plastic a big number of ribs 4 run out. At the base they can be for instance 0.15 millimetres wide and one millimetre high. They have an outward narrowing form. The ribs are placed close to each other in parallel rows. The ribs have a rounded transition at the base.

[0009] After manufacturing the foil can be rolled on rolls. Protective paper which can be pulled off is not necessary since the edges of the ribs reach the self-adhesive layer when rolled up.

[0010] Instead of a self-adhesive glue, the inside can consist of a non-woven material which is well fastened to the carrying foil. The non-woven material can easily be glued and in this case it is the intention that the object which is to be protected or the foil can be provided with glue and that after that the foil is pressed on to the object. If the foil is to be suitable for small boats, for instance pleasure boats of plastic where the surface of the hull is strongly curved, the foil can be a little elastic, which many plastics allow. In order to prevent air-bubbles between the hull and the foil, the foil can be perforated.

[0011] The production of the foil can be made so that a laminate of carrying foil of not thermoplastic material or of a plastic with a high melting point is laminated with a thermoplastic with a low melting point. The laminate is heated and pressed against a rotating cylinder provided with many grooves in which plastic material is pressed out and forms ribs. After the plastic has come into the grooves the plastic is cooled and when the carrying foil is rolled off from the cylinder the ribs leave the grooves.

[0012] It is possible to make a foil with projecting narrowing ribs also in other ways, for instance by chemical etching.

[0013] It is evident that the foil can be given various shapes with regard to the use of material, the distance between the ribs, height, thickness, inclination and cross-section of the ribs.

[0014] If the foil is strong it is possible, after long use, to pull off the foil from a hull.

[0015] Unlike attaching loose fibres to a surface where many fibres are slanting and the distance between the fibres is not controlled, the ribs can be made to be at right angles to the surface and with an equal distance between them. Because the ribs are made by pressing from a foil they are safely connected with it and cannot come loose. Owing to the outward narrowing form they are strong and owing to the open form the foil can be easily cleaned.

[0016] In FIG. 2 the ribs are indicated by 5, They were made directly on a hull 6. This can be made by rolling a cylinder of adjacent round razor blades under pressure against the surface which has first been smeared with the material which is to form the ribs. The rolling can be made with a cold cylinder on a polymer which has not had time to harden or with a heated cylinder on a hardened polymer.

[0017] On ships the ribs should be parallel with the surface of water to make friction against the water low. This direction also gives the best anti-fouling effect since it disturbs the wandering of the larvae towards the light.

[0018] Experiments have been made with a rib structure where the angles at the base were 79 degrees. This surface reduced the fouling of acorn barnacles with 98 per cent compared with a smooth control surface.

[0019] A great height of the ribs affects the friction against the water negatively. For stationary objects for instance off-shore and sea breeding the height of the ribs is of little importance.

[0020] For pipes longitudinal ribs inside and outside can be made by extrusion. 

1. Structure that counteracts biofouling in aquatic environments, characterized by the fact that the surface of an object has ribs projecting from it, situated close to each other (4, 5), which are narrowing outward and whose height is less than two millimetres.
 2. Structure according to Patent claim 1, characterized by the fact that each rib has a cross-section in the main triangular with the angles at the base larger than 70 degrees.
 3. Structure according to an earlier patent claim, characterized by the fact that the ribs are made from a foil which is meant to be glued on the object which is to be protected.
 4. Structure according to Patent claim 3, characterized by the fact that the foil on its inside has a carrying layer of other material than the foil and where the carrying layer is meant to be glued on the object which is to be protected.
 5. Structure according to Patent claim 1, characterized by the fact that it is made with a cold or warm tool directly on the surface of the object which is to be protected.
 6. Structure according to Patent claim 1, characterized by the fact that it is made by chemical etching directly on the surface which is to be protected.
 7. Structure according to Patent claim 1, characterized by the fact that it is made by chemical etching on a foil which is glued on the object which is to be protected.
 8. Structures according to Patent claim 1, characterized by the fact that it is made on pipes by extrusion. 